For the purpose of simplifying the connection of several electrical devices (e.g. mechanical or electronic motor control units or contactors) to a voltage source (e.g. a 3-phase a.c. system), the devices are often connected to the voltage source in combinations, by way of a busbar. For this purpose, the busbar usually comprises fixed-position contact pins, by which electrical contact is effected to the appropriate conductor connectors on the devices. The use of a busbar enables the time-consuming individual wiring of the devices to be eliminated.
Electrical connection of devices by way of a busbar is also referred to as combination structuring. In the case of switchgear, a combination is generally implemented using a rigid supply feed system (busbar). Important advantages of such a system are the reduction in the wiring effort, and the avoidance of wiring errors.
If individual devices are attached onto a top-hat rail and connected via a busbar, a critical disadvantage of such a linkage is that the withdrawal of an individual device, or the exchange of a device, can only be effected by the complete disassembly of the busbar, because only in this indirect way can the devices be individually taken off the top-hat rail again. For example, if a combination of five devices is attached to a top-hat rail, and if each of the devices is connected to contact pins on the busbar by three conductor connectors, each of which is in the form of a screw conductor connector, then, if a device replacement is necessary for one of the five devices, the busbar must first be disassembled. In order to remove the busbar, 15 screws on the conductor connectors must first be undone. After the removal of the busbar, the device can then be exchanged and the combination must then be reconnected to the busbar. For this purpose, all 15 screws must be tightened up.